Assembling the Freeduino Serial v2.0 Board (MAX232)

Assembling the ArduinoTM Diecimila Compatible Freeduino Serial v2.0 Board

SCHEMATICS (click on images to enlarge)
freeduino serial schematic

The Arduino diecimila compatible Freeduino serial board is a special version of the Arduino serial board designed by NKC Electronics. The board is diecimila compatible (autoreset) and includes the 13 digital pin LED for easy diagnostics and basic LED sketch execution. The v2.0 board uses a MAX232 compatible chip for interfacing with RS232. The older v1.0 board used two transistors, but had some reliability issues with auto-reset and sketch uploading.
First, unpack the kit

freeduino serial KIT

and start with the PCB.

Let’s start with the power portion of the schematic using the following parts:

DC1 DC power jack
D1 1N4004 diode
C5 100nF ceramic capacitor
C6, C7 47uF (or 33uF or 22uF) electrolytic capacitor
IC2 7805 5V positive voltage regulator
Power LED 3mm LED
R2 330 ohm resistor

Freeduino serial KIT

Plug a wall plug voltage regulator (+7V to +12V). The LED lights up, indicating that the Power supply is working.
NOTE: This board is shields friendly as the 7805 voltage regulator is mounted horizontally.

Next continue with the soldering of the RS232 components:

Freeduino serial KIT

X1 DB9 female PCB adapter
IC3 16-pin IC socket
C4, C8, C9, C10, C11, C12 0.1uF (100nF) ceramic capacitors

Solder the rest of the components:

Freeduino serial KIT

R3 1.5Kohm resistor
R4, R6 1 Kohm resistor
R5 10 Kohm resistor
C2, C3 22pF ceramic capacitor
C1 0.1uF (100nF) ceramic capacitor
13 3mm LED (Arduino pin 13 status LED)
Q1 16 MHz crystal
RESET Reset switch
IC1 28-pin IC socket
ICSP 2×3 pin male header

Now solder the headers and sockets:

POWER & Analog In 6-pin female header
Digital 2 x 8-pin female header

Freeduino serial KIT

Pay special attention to the alignment of the female headers.

Freeduino serial KIT

And finally install the ATMEGA168/ATmega328P MCU and the MAX232 (or HIN232 / ICL232 / ICL3232) chips.

Freeduino serial KIT

Freeduino serial KIT

The board is ready to be used. Start the Arduino IDE and load the BLINK sketch from the examples directory. Verify that ATMEGA168 (or Duemilanove with ATmega328) is selected in Tools –> Microcontroller (MCU) and Arduino Diecimila in the Tools –> board option. Select the COM port number corresponding to the serial interface where the Freeduino serial board is connected to. Press the “Upload to I/O board” button in Arduino and the board should autoreset and complete the programming. If you selected correctly the BLINK sketch, the LED “13” must start blinking once every 2 second (0.5Hz).

The board has space for an optional 3.3V regulator (78L33 TO-92 footprint) with it’s associated decoupling 0.1uF capacitor (C13).

Freeduino serial KIT

3 Responses to “Assembling the Freeduino Serial v2.0 Board (MAX232)”

  1. Rob Hart says:

    Hello NKC Electronics,

    I have just purchased one of these boards and really like the work you have put into it, a very nice product!

    One question, if i didn’t want the “Auto-Reset” feauture am i correct in saying that you just don’t install the C4 (0.1uF (100nF)) ceramic capacitor?

    Many Thanks Rob.

  2. Eric Shattow says:

    Looking at the schematic, C4 is indeed the auto-reset capacitor. Leaving the auto-reset cap N/C is useful for some soft flow control applications. Use the reset button and the bootloader will allow code to be uploaded within a short period of time.

  3. Goat says:

    Nice board. Assembled in about an hour (eyes are going on me it seems), and once I figured out that the cable is wired straight through pin to pin, it fired right up and works flawlessly. Hope you get some more bare boards in. Probably the old school in me, but I really like the serial interface. Need some boards farmed out for assembly, can do. : )